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Wed, 25 Jun 2025 17:02:52 -0700 (PDT) Date: Wed, 25 Jun 2025 20:02:50 -0400 From: Yury Norov To: Shrikanth Hegde Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, tglx@linutronix.de, maddy@linux.ibm.com, vschneid@redhat.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, kprateek.nayak@amd.com, huschle@linux.ibm.com, srikar@linux.ibm.com, linux-kernel@vger.kernel.org, christophe.leroy@csgroup.eu, linuxppc-dev@lists.ozlabs.org, gregkh@linuxfoundation.org Subject: Re: [RFC v2 4/9] sched/fair: Don't use CPU marked as avoid for wakeup and load balance Message-ID: References: <20250625191108.1646208-1-sshegde@linux.ibm.com> <20250625191108.1646208-5-sshegde@linux.ibm.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250625191108.1646208-5-sshegde@linux.ibm.com> On Thu, Jun 26, 2025 at 12:41:03AM +0530, Shrikanth Hegde wrote: > Load balancer shouldn't spread CFS tasks into a CPU marked as Avoid. > Remove those CPUs from load balancing decisions. > > At wakeup, don't select a CPU marked as avoid. > > Signed-off-by: Shrikanth Hegde > --- > while tesing didn't see cpu being marked as avoid while new_cpu is. > May need some more probing to see if even cpu can be. if so it could > lead to crash. > > kernel/sched/fair.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 7e2963efe800..406288aef535 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8546,7 +8546,12 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags) > } > rcu_read_unlock(); > > - return new_cpu; > + /* Don't select a CPU marked as avoid for wakeup */ > + if (cpu_avoid(new_cpu)) > + return cpu; > + else > + return new_cpu; > + > } There are more 'return's in this function, but you patch only one... > > /* > @@ -11662,6 +11667,9 @@ static int sched_balance_rq(int this_cpu, struct rq *this_rq, > > cpumask_and(cpus, sched_domain_span(sd), cpu_active_mask); > > + /* Don't spread load into CPUs marked as avoid */ > + cpumask_andnot(cpus, cpus, cpu_avoid_mask); > + > schedstat_inc(sd->lb_count[idle]); > > redo: > -- > 2.43.0